Let it be remembered that the state of spiritual solitude does not exclude all thoughts from the mind; but only those which are its own, which are self-originated, and which tend, therefore, to dissociate it from God. Accordingly, it does not exclude those thoughts, to what ever subjects they may relate, of which God may properly be regarded as the author. And it is proper to say here, in order to determine what thoughts are from God and what are not, that thoughts which are from God are characterized by this mark, in particular, that they always harmonize with the arrangements of his providence. Thoughts, which arise from the instigations of self, and not from a divine movement, are not in harmony with what God in his providential arrangements would desire and choose to suggest; but, on the contrary, they busy themselves with recollections and images of persons, things, and plans, which are wholly inconsistent with such arrangements. All conceptions of persons, things, and situations, all imaginations, all thoughts, and all reasonings, which, in coming in our own will, are out of harmony with the existing providential arrangements are not only not from God, but they constitute so many disturbing influences, which separate God from the soul. The evil is inexpressibly great. In the truly holy soul, which, after many temptations and hesitancies, is fully established in the way of holiness, thoughts so discordant and out of place are not permitted to enter. It stands apart, if one may so express it, constituting an unoccupied space, a closet shut up, a still and sacred seclusion, unapproachable to everything which comes unbidden by its great Master.
— edited from A Treatise on Divine Union (1851) Part 6, Chapter 10.